Multiple patterning are lithography techniques that enable reduction of the feature size, such as Self-Aligned Double Patterning (SADP), or in general Self-Aligned Multiple Patterning (SAMP), litho-etch litho-etch (LELE) or in general multiple LE and litho-litho etch (LLE), which have become standard vernacular for near term semiconductor processing. In Self-Aligned Multiple Patterning (SAW), original elements (e.g., linear elements) are split to two or more separate features (e.g., by deposition and etching), termed features or spacers, which are used to produce smaller features using process steps.
However, the splitting methods may incur process variations that might cause “pitch walk”, e.g., as a by-product of line critical dimension (CD) and spacer error (in SADP) or overlay variations (in LELE), which affects the later steps, for example, different etched depths due to loading effects. The term “pitch walk” as used herein in this application for SAMP, is defined, in a multiple patterning process, as the difference in spaces between a couple of adjacent features or spacers formed on two sides of the same resist line, versus a couple of adjacent features or spacers formed on two sides of the same space between two adjacent resist lines. For LELE (or LLE) “pitch walk” is the difference in distance between a feature and a feature next to it on its left side vs. a feature next to it on its right side. Currently the main tool for pitch walk measurement is CD-SEM, which is a relatively slow and expensive tool.